Adjustable air filter

ABSTRACT

An adjustable air filter for use in heating, ventilating, cooling, and forced air systems. The air filter includes a media for filtering air and adapted to be cut with scissors, and a frame embracing the peripheral edges of the media. The frame includes a pair of male sections and a pair of female sections respectively telescopingly receiving the male sections. Also, the frame is adapted to be cut with scissors and is preferably formed of polyvinyl chloride. Each of the male sections includes a T-shaped projection and each of the female sections includes a complementary shaped T-shaped slot adapted to telescopingly receive the T-shaped projection for preventing inward separation of the sections from one another. In the preferred form the media is of the electrostatic type and includes at least one layer of polypropylene woven in an egg-crate pattern. Also, the layer preferably includes a pad of washable polyester material. At least one grid, having squares defining interstices, is formed of polypropylene and is heat staked into the layer of polypropylene for permanent attachment thereto. Self-tapping screws are provided to lock the sections of the frame together against telescoping separation thereof.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates, in general, to air filters, and inparticular to an air filter for use in heating, ventilating, cooling,and forced air systems

2. Information Disclosure Statement

There are typically relatively few popular sizes, e.g., five, of airfilters used in homes and the like. On the other hand, there is a needfor many different odd size filters. The problem generally occurs whencontractors build a house. Rather than building the opening for thefilter a standard size, a great many of the contractors will cut thesize hole for whatever is convenient for them to cut. There areadjustable frames on the market in which one channel is telescopicallyreceived within another which may be relevant prior art to the presentinvention. However, none of these frames are completely satisfactory forone reason or another, for example, the telescoping channels are flimsyand difficult to assemble.

It is, therefore, desirable to have an air filter which is sturdy andeasy to assemble.

A preliminary patentability search in Class 55, subclasses 501, 496,503, 506, 511, 516, 481, 482 and digest 31, and Class 160, subclasses372, 373 and 374, produced the following patents, some of which may berelevant to the present invention: Sweeney, U.S. Pat. No. 1,122,437,issued Dec. 29, 1914; Lichtman, U.S. Pat. No. 2,175,903, issued Oct. 10,1939; Lewis, U.S. Pat. No. 2,802,544, issued Aug. 13, 1957; Bell, U.S.Pat. No. 3,274,759, issued Sept. 27, 1966; Weed, U.S. Pat. No.3,675,402, issued Jul. 11, 1972; and Pick, U.S. Pat. No. 5,059,218,issued Oct. 22, 1991.

While each of the above patents disclose various filters and screens,none disclose or suggest the present invention. More specifically, noneof the above patents disclose or suggest an air filter for use inheating, ventilating, cooling, and forced air systems in which anadjustable frame formed of a material adapted to be cut by a cuttingdevice comprises at least one female section having at least one leg; atleast one male section having at least one leg telescopingly mated withsaid female section; coacting means on said leg of said female sectionand on said leg of said male section for permitting lengthwisetelescoping movement of said leg of said mate section and said leg ofsaid female section relative to one another and yet preventing inwardseparation of said leg of said female section from said leg of said malesection; and locking means for locking said leg of said female sectionand said leg of said male section in a fixed assembled position relativeto one another.

Sweeney, U.S. Pat. No. 1,122,437 discloses a screen that is adjustablein one direction to fit a window. The end portions of the screen areprovided with dovetailed tongues which can be gripped by the endportions of the side strips.

Lichtman, U.S. Pat. No. 2,175,903 discloses an adjustable air filterwhich may be adjusted as to size and attached to various types of hotair registers in homes, offices, and other buildings. The frame is madeof four L-shaped sections formed as channel members which telescope withadjacent channel members. There are wing screws to hold the telescopingsections in predetermined positions. The sections are provided withbarbs intended to permit the filter element t be impaled thereon.

Lewis, U.S. Pat. No. 2,802,544 discloses a filter screen for fluidswherein the filtering medium is a brush or a plurality of brushes. Thefilter has a four sided rectangular metal frame with each side being inthe form of a channel. The filter screen further comprises rectangularfront and rear sheets of expanded metal. The assembly is held in placewithin the frame by four clamping plates having wing nuts for holdingthe clamping plates in position.

Bell, U.S. Pat. No. 3,274,759 discloses an adjustable frame structurefor air filters and the like adapted for use as window screens orventilators. The adjustable frame structure includes a first and secondgenerally rectangular frame with each frame including a pair of railsand a pair of end-frame members. Each of the rails has a key-retainingguideway therein. One end frame member of each of the frames has a pairof key members slidably retained in the guideway of the other frame andlongitudinally slidable to hold the two frames in confronting,overlapping slidable relationship.

Weed, U.S. Pat. No. 3,675,402 discloses an adjustable filter assemblyadapted to be inserted in apertures of buildings such as windows ordoors or the like. The frame assembly is telescopically adjustable intwo different directions and is provided with a clamp for holding theadjustment at any desired predetermined size or shape within theconfines of its adjustment limits.

Pick, U.S. Pat. No. 5,059,218 discloses a construction for supporting aflexible screen or sheet such as a window screen, or the like, and itsapplication to the assembly of an electrostatic air filter of thecharged media type. The filter includes a U-shaped channel adapted toreceive a spline member for frictionally engaging a flexible sheet suchas a window screen.

SUMMARY OF THE INVENTION

The present invention is a permanent type air filter for use in heating,ventilating, cooling, and forced air systems. The filter includes amedia having its edges received in and supported by a trimable channelframe, which has two male sections telescopically coacting with twofemale sections to permit size variations, both horizontally andvertically, by cutting the media and adjusting the frame to the desiredsize. The frame has T-shaped sections and complementary shaped slotstelescopically receiving the projections for providing sturdiness to theframe. After the desired size is obtained, self tapping screws areinstalled to make the size permanent. Then, subsequently, if it isdesired to open the frame, the screws are removed.

In the preferred embodiment, the media includes two layers of wovenfabric in an egg-crate pattern and formed of polypropylene material. Onelayer of material is on the inlet side of the filter and the other layeris on the discharge side thereof. The center of the media includes awashable polyester pad sandwiched between the two layers ofpolypropylene material. It will be understood that the media may be anyother type without departing from the spirit and scope of the presentinvention.

It is an object of the present invention to provide a sturdy andimproved permanent type air filter for use in heating, ventilating,cooling, and forced air systems which has an easily trimmed media andeasily adjusted frame. On the other hand, if a smaller frame is desired,the frame can be cut to a smaller size.

A further object is to provide an improved media assembly of theelectrostatic type which includes grids having enlarged squaresestablishing interstices and with the grids being respectively heatstaked onto the electrostatic components.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front elevational view of the assembled filter of thepresent invention.

FIG. 2 is an enlarged fragmentary sectional view taken as on the line2--2 of FIG. 1.

FIG. 3 is a view of the filter of FIG. 1 shown in a disassembleddisposition.

FIG. 4 is an enlarged sectional view taken as on the line 4--4 of FIG.3.

FIG. 5 is an enlarged sectional view taken as on the line 5--5 of FIG.3.

FIG. 6 is an enlarged sectional view taken as on the line 6--6 of FIG. 3with the media being shown in a disassembled relationship.

FIG. 7 is a view similar to FIG. 6 but showing the media in an assembledrelationship.

FIG. 8 is an enlarged side elevational view of a portion of the frameshowing the V-shaped cut therein to provide the means for forming acorner of the frame.

FIG. 9 is an enlarged sectional view taken as on the line 9--9 of FIG.1.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to the drawings, the filter 11 of the present inventionincludes in general a filter media 13 and a frame 15. When filter 11 isin an assembled condition, as shown in FIG. 1, frame 15 surrounds theperipheral outer edge portions 17 of media 13 to support the media.

In the preferred form, media 13 is an electrostatic type and preferablyincludes a pair of electrostatic layers 19, 21, of a construction wellknown to those skilled in the art, and a center pad 23 disposed betweenlayers 19, 21. However, it will be understood that media 13 may be anyother type without departing from the spirit and scope of the presentinvention.

Filter 11 is symmetrical so that either side can be the air inlet sidewith the opposite side being the air outlet side. However, for purposesof clarity, the side 25 will be considered the inlet side and side 27the outlet side. Thus, layer 19 is on the inlet side 25 of filter 11 andlayer 21 is on the outlet side 27 of the filter 11. In other words, theair being filtered passes through the filter 11 from the left as viewedin FIG. 9 to the right thereof, i.e., from inlet side 23 through thefilter 11 and out the outlet side 27.

Layers 19, 21 are preferably identical in construction and the followingdescription of layer 19 will suffice for both. Layer 19 consists ofwoven fabric of an egg-crate pattern well known to those skilled in theart and is preferably formed of a polypropylene material. As is known bythose skilled in the art, polypropylene attracts microsize particlesdown to 1, 2 and 3 micron size. The layer 19 is the same on both sidesand functions in the same manner regardless of which face of the layer19 is turned towards the oncoming air. In the assembled condition, thecenter pad 23 is sandwiched between layers 19, 21, as best seen in FIGS.7 and 9. Center pad 23 in the preferred form consists of a washablepolyester pad of approximately 1/2 inch (1.27 cm) in thickness.

Layer 19 is covered on the inlet side 25 with a grid 29 having amultiplicity of squares 31 made of polypropylene. The squares arepreferably approximately 1 inch (2.54 cm) by 1 inch (2.54 cm) and eachsquare 31 is formed of four legs 33 which are shared with adjacentsquares to establish interstices 35 with each being formed by four ofthe legs 33 and through which the air passes. Grid 29 is for stiffeningpurposes and is permanently attached to layer 19, preferably by stakingthe grid 29 to the layer 19 by the following means.

At each of the intersections of legs 33, is provided a pointed pin 37extending inwardly towards layer 19, as best seen in FIG. 6. In theassembly of grid 29 with layer 19, grid 29 is brought into contact withlayer 19 whereupon pins 37 extend through the woven fabric of layer 19and to the opposite side thereof. The distal ends of pins 37 are broughtinto contact with heat and pressure whereupon buttons 39 are formed sothat when the polypropylene cools, a permanent attachment is providedbetween the layer 19 and the grid 29.

The layer 21 and grid 43 are permanently attached to one another in thesame manner as heretofore described relative to layer 19 and grid 29 sothat the pointed ends of pins 45 on grid 43 are formed into buttons 46.

Frame 15 includes two male sections 47, 49, which are preferablyidentical with one another, and two female sections 51, 53 which arealso preferably identical with one another. Since male sections 47, 49are identical, the following description of male section 47 will sufficefor both. Male section 47 is channel-shaped along the entire lengththereof except for the corner 55 as will be understood in thedescription to follow. Thus, male section 47 includes a web 57 andspaced flanges 59, 61 respectively integrally formed with the edges ofweb 57 and extending perpendicularly therefrom as best seen in FIG. 4.Male section 47 includes a projection 63 extending longitudinally ofmale section 47 along the entire length thereof except for the corner55, as will be better understood in the description to follow.Projection 63 in cross section, as seen in FIG. 4 is preferably T-shapedand includes a stem 65 integrally attached to web 57 at the innersurface 67 thereof and which stem extends perpendicularly from the innersurface. Projection 63 includes laterally extending portions 69extending outwardly in opposite directions from the distal or oppositeend of stem 65 from surface 67. Portions 69 are preferably integrallyattached to stem 65 and stem 65 is preferably integrally attached to web57.

Male section 47 is preferably extruded and formed of PVC (polyvinylchloride). Thus, male section 47 is preferably integrally formed intoone piece of material which is cut to the desired length. Intermediatethe opposite ends 71, 73 of male section 47 a V-shaped cut 75 isprovided in male section 47 through the flanges 59, 61. The V-shaped cut75 is preferably formed with the sides of the cut extendingsubstantially perpendicularly to one another, as best seen in FIG. 8, sothat male section 47 may be bent to establish corner 55. It will beunderstood that the V-shaped cut 75 is cut through the T-shapedprojection 63 but not through the web 57 so that web 57 may be bent tothe above described perpendicular relationship and T-shaped projection63 will not interfere with the bending thereof. In other words, theportion of the web 57 at the .[.appex.]. .Iadd.apex .Iaddend.or bottomof the V-shaped cut 75 acts as a hinge to permit the bending of theportions of male section 47 to the perpendicular relationship shown inFIG. 3.

Since female sections 51, 53 are identical with one another, thefollowing description of female section 51 will suffice for both. Femalesection 51 is channel-shaped along the entire length thereof except forthe corner 76 as will be understood in the description to follow. Thus,female section 51 includes a web 77 and spaced flanges 79, 81respectively integrally formed with the edges of web 77 and extendingperpendicularly therefrom as best seen in FIG. 5. Female section 51includes a slot 83 extending longitudinally of female section 51 alongthe entire length thereof except for the corner 76, as will be betterunderstood in the description to follow. Slot 83 in cross section, asseen in FIG. 5, is preferably T-shaped and is preferably formed in a rib85 integrally attached to web 77 and extending inwardly therefrom. Slot83 includes a narrow portion 87 extending inwardly through web 77 fromthe outside thereof and includes portions 89 communicated with the innerend of narrow portion 87 and extending laterally in opposite directionstherefrom. Thus, slot .[.87.]. .Iadd.83 .Iaddend.is complementary shapedand sized relative to projection 63 to closely telescopically receiveprojection 63 as best seen in FIG. 2.

Female section 51 is preferably extruded and formed of PVC (polyvinylchloride). Thus, female section 51 is preferably integrally formed intoone piece of material which is cut to the desired length. Intermediatethe opposite ends 91, 93 of female section 51 is provided a V-shaped cutlike V-shaped cut 75 in female section 51 through flanges 79, 81. Aswith the V-shaped cut 75 the V-shaped cut in female section 51 ispreferably formed with the sides of the cut extending substantiallyperpendicularly to one another so that female section 51 may be bent toestablish corner 76 in the same manner that corner 55 was established asheretofore described.

From the foregoing it will be understood that each of the sections 47,49, 51, and 53 when bent at the corners thereof have legs which areperpendicular to one another. Thus, first male section 47 has legs 95,97 which are perpendicular, second male section 49 has legs 99, 101which are perpendicular, first female section 51 has legs 103, 105 whichare perpendicular, and second female section 53 has legs 107, 109 whichare perpendicular.

The lengths of the male sections 47, 49 and female sections 51, 53 aremade long enough so that the largest or maximum size filter that iscontemplated can be accommodated. Thus, for example, in most cases a 20inch (50.8 cm) by 25 (63.5 cm) inch filter size will be large enough,but, of course, if desired, it could be larger. The lengths of theindividual male sections, 47, 49 and female sections 51, 53 aredetermined by the maximum size of filter desired and so that the distalends of the male and female sections will overlap a sufficient amount,as for example, by several inches in order that the filter will besturdy. It is contemplated that the media 13 will be of a size to matchthe maximum size of the frame 15 and that the components of the mediawill be substantially the same size. In other words, electrostaticlayers 19, 21 with the grids 29, 43 attached thereto and the center pad23 will all be of the same size which is adapted to fit into the maximumsize frame 15.

Also, it is contemplated that the customer will buy a kit of partsincluding the male sections 47, 49, female sections 51, 53, and media13; and would then cut the components down from the maximum size.However, if the maximum size were the size desired, there would be noneed for any trimming to take place, and if the legs of the frame 15were of such lengths that the frame 15 could be telescoped down to thedesired size then there would be no need to cut frame 15. It should bepointed out that the media 13, as well as the components of frame 15,are easily cut with cutting devices. Thus, media 13 is easily cut withscissors or the like and frame 15 is easily cut with a heavier cuttingdevice such as cutting snips, shears or the like. Then, after the media13 and frame 15 is either cut or telescoped down to the desired size,the filter is assembled around the edges 17 of media 13 so that theedges of the media are embraced and held by the frame 15. It will beunderstood that in the above step, the distal ends 71, 73, 113, and 117of the male sections 47, 49 are respectively telescoped with the distalends 93, 111, 115, and 91 of the female sections 51, 53. Thus, forexample, end 71 of male section 47 is aligned with end 93 of femalesection 51 and the two are brought together so that projection 63extends into T-slot 83 with flanges 59, 61 of male section 47 beingrespectively on the outside of flanges 81, 79 of female section 51, andwith web 57 of male section 47 being on the outside of web 77 of femalesection 51 so that the male section 47 and female section 51 may beslidingly telescoped together until the desired length of the frame isreached in which the end edges 17' of the media 13 is embraced and heldby the respective male section 47 and female section 51. When the frame15 is telescoped down to the desired size embracing the respective edges17, 17' of the media 13, the female and male sections aresemi-permanently attached together preferably by means of screws 119(only one of which is shown), but there is preferably a screw 119 ateach of the overlapped portions of the legs 95, 97, 99, 101, 103, 105,107, and 109 of male and female sections 47, 49, 51, and 53. Toaccomplish the above mentioned attachment by screws 119, a hole 121 ispreferably provided adjacent each of the ends 71, 73, 113 and 117 ofmale sections 47, 49. The attachments at each of the four abovementioned overlapped portions are preferably substantially alike and thefollowing description relative to the attachment at the overlappedportions of legs 95 and 103 should suffice for all. Hole 121 extendsthrough web 57 and is preferably spaced approximately one inch from thedistal end of leg 95. Screw 119 may be inserted through hole 121. Sincescrew 119 is self tapping, when it is turned, it will rupture rib 85 offemale section 51, as seen in FIG. 9, so that legs 95 and 103 are lockedtogether. Then, if it is ever desired to disassemble filter 11, thescrews 119 may be removed.

From the foregoing it will be apparent with the coaction of theprojections 63 in sections 47, 49 and the slots 83 in sections 51, 53, avery, sturdy and rigid filter 11 is provided which is easy to assemble.Thus, the coaction of the projections 63 and slots 83 permits lengthwisetelescoping movement of the legs of the male sections and the legs ofthe female sections relative to one another and yet prevent inwardseparation of the legs of the female sections from the legs of the malesections. It will be understood that when the term "preventing inwardseparation" is used herein it will be deemed to mean preventing theseparation of the legs of the female sections from the legs of the malesections in a direction toward the center of the filter, i.e., in adirection which extends perpendicular to the longitudinal axes of thelegs of the sections. Also, there is provided a filter 11 which is veryefficient in operation due to the large interstices 35 and which can beeasily trimmed to size due to the narrow legs 33 of the squares 31 aswell as the ease of trimming or cutting due to the materials used in themedia 13 and frame 15.

Although the present invention has been described and illustrated withrespect to a preferred embodiment and a preferred use therefor, it isnot to be so limited since modifications and changes can be made thereinwhich are within the full intended scope of the invention.

I claim:
 1. An air filter for use in heating, ventilating, cooling, andforced air systems, said air filter including an adjustable frame havingfour sides, said frame comprising:(a) at least one female section havingat least one channel-shaped leg; (b) at least one male section having atleast one channel-shaped leg telescopingly mated with said femalesection to establish one of said sides of said frame; (c) coacting meanson said leg of said female section and on said leg of said male sectionfor permitting lengthwise telescoping movement of said leg of said malesection and said leg of said female section relative to one another andyet preventing inward separation of said leg of said female section fromsaid leg of said male section, said coacting means including a T-shapedprojection attached to said male section and extending longitudinally ofsaid male section and a slot in said female section extendinglongitudinally of said female section, said slot being complementaryshaped and sized relative to said projection for closely telescopicallyreceiving said projection; and (d) locking means for locking said leg ofsaid female section and said leg of said male section in a fixedassembled position relative to one another.
 2. The air filter of claim 1in which said male section and said female section are formed ofpolyvinyl chloride.
 3. An adjustable air filter for use in heating,ventilating, cooling, and forced air systems, said air filtercomprising:(a) media means for filtering air, said media means having aperipheral edge; and (b) frame means embracing said peripheral edge ofsaid media means; said frame means including:(i) a pair of femalesections each having a channel-shaped first leg and a channel-shapedsecond leg perpendicular to said first leg; (ii) a pair of male sectionseach having a channel-shaped first leg and a channel-shaped second legperpendicular to said first leg, said first legs of said male sectionsbeing respectively telescopingly mated with said second legs of saidfemale sections and said second legs of said male sections beingrespectively telescopingly mated with said first legs of said femalesections to establish four sides to said frame means; and (iii) coactingmeans on said first and second legs of said female sections and on saidfirst and second legs of said male sections for permitting telescopingmovement of said first legs of said male sections and said second legsof said female sections relative to one another and yet preventinginward separation of said first legs of said female sections from saidsecond legs of said male sections and preventing inward separation ofsaid second legs of said female sections from said first legs of saidmale sections, said coacting means including T-shaped projectionsrespectively attached to said male sections and extending longitudinallyof said male sections to which .Iadd.said projections are.Iaddend.attached and slots respectively in said female sectionsextending longitudinally of said female sections, said slots beingcomplementary shaped and sized relative to said projections for closelytelescopically receiving said projections.
 4. The air filter of claim 3in which said male sections and said female sections are formed ofpolyvinyl chloride.
 5. The air filter of claim 3 in which said mediameans includes at least one electrostatic layer and at least one gridincluding a multiplicity of squares having intersecting legsestablishing interstices for the passage of air therethrough.
 6. The airfilter of claim 5 which includes button means for permanently attachingsaid grid to said layer.
 7. An adjustable air filter for use in heating,ventilating, cooling, and forced air systems, said air filtercomprising:(a) media means for filtering air, said media means having aperipheral edge and said media means being formed of a material as maybe cut with scissors; and (b) a frame formed of a material as may be cutwith scissors, said frame embracing said peripheral edge of said mediameans and including:(i) a first female section having a first leg and asecond leg substantially perpendicular to said first leg of said firstfemale section, said first female section being channel-shaped in crosssection and each leg thereof including a web and a pair of spacedflanges; (ii) a second female section having a first leg and a secondleg substantially perpendicular to said first leg of said second femalesection, said second female .[.second.]. .Iadd.section .Iaddend.beingchannel-shaped in cross section, and each leg thereof including a weband a pair of spaced flanges; (iii) a first male section having a firstleg and a second leg substantially perpendicular to said first leg ofsaid first male section, said first male section being channel-shaped incross section, and each leg thereof including a web and a pair of spacedflanges, said first leg of said first male section being telescopicallymated with said second leg of said first female section for movement ofsaid first leg of said first male section and said second leg of saidfirst female section lengthwise relative to one another with said web ofsaid first leg of said first male section being adjacent said web ofsaid second leg of said first female section, and said second leg ofsaid first male section being telescopically mated with said first legof said second female section for movement of said second leg of saidfirst male section and said first leg of said second female sectionlengthwise relative to one another with said web of said second leg ofsaid first male section being adjacent said web of said first leg ofsaid second female section; (iv) a second male section having a firstleg and a second leg substantially perpendicular to said first leg ofsaid second male section, said second male section being channel-shapedin cross section, and each leg thereof including a web and a pair ofspaced flanges, said first leg of said second male section beingtelescopically mated with said second leg of said second female sectionfor movement of said first leg of said second male section and saidsecond leg of said second female section lengthwise relative to oneanother with said web of said first leg of said second male sectionbeing adjacent said web of said second leg of said second femalesection, and said second leg of said second male section beingtelescopically mated with said first leg of said first female sectionfor movement of said second leg of said second male section and saidfirst leg of said first female section lengthwise relative to oneanother with said web of said second leg of said second male sectionbeing adjacent said web of said first leg of said first female section;(v) coacting means on said first and second female sections and on saidfirst and second male sections for permitting telescoping movement ofsaid first and second female sections and yet for preventing inwardseparation of said first leg of said first female section from saidsecond leg of said second male section, for preventing inward separationof said second leg of said first female section from said first leg ofsaid first male section, for preventing inward separation of said firstleg of said second female section from said second leg of said firstmale section, and for preventing inward separation of said second leg ofsaid second female section from said first leg of said second malesection, said coacting means including T-shaped projections respectivelyattached to said male sections and extending longitudinally of the malesections to which .Iadd.said projections are .Iaddend.attached; ribsrespectively attached to said female sections and extending inwardlyfrom said webs of said female sections; and T-shaped slots respectivelyin said female sections extending through said webs of said femalesections and into said ribs; said slots being complementary shaped andsized relative to said projections for closely telescopically receivingsaid projections; and (vi) locking means for locking said first andsecond female sections and said first and second male sections in fixedassembled position relative to one another.
 8. The air filter of claim 7in which said locking means includes at least one aperture through saidweb of one of said female sections and at least one self-tapping screwextending through said aperture, through said T-shaped slot of said oneof said female sections and into said rib of said one of said femalesections.
 9. The air filter of claim 8 in which said male sections andsaid female sections are formed of polyvinyl chloride such as may be cutto any desired length; in which said media includes at least oneelectrostatic layer formed of polypropylene such as may be cut to anydesired size and a pad formed of washable polyester such as may be cutto any desired size; in which is included at least one grid formed ofpolypropylene such as may be cut to any desired size; and in whichpolypropylene attachment means is provided for permanently attachingsaid grid to said electrostatic layer.
 10. An adjustable frame for usein heating, ventilating, cooling, and forced air systems, said framehaving four sides and comprising:(a) at least one female section havingat least one channel-shaped leg; (b) at least one male section having atleast one channel-shaped leg telescopingly mated with said femalesection to establish one of said sides of said frame; (c) coacting meanson said leg of said female section and on said leg of said male sectionfor permitting lengthwise telescoping movement of said leg of said malesection and said leg of said female section relative to one another andyet preventing inward separation of said leg of said female section fromsaid leg of said male section, said coacting means including a T-shapedprojection attached to said male section and extending longitudinally ofsaid male section and a slot in said female section extendinglongitudinally of said female section, said slot being complementaryshaped and sized relative to said projection for closely telescopicallyreceiving said projection; and (d) locking means for locking said leg ofsaid female section and said leg of said male section in a fixedassembled position relative to one another. .Iadd.
 11. An air filter foruse in forced air systems, comprising:a filter media for filtering air,the filter including at least a first thermoplastic electrostatic layerand at least a first thermoplastic stiffening grid having intersticesfor the passage of air therethrough; and at least one heat and pressureformed connection that permanently attaches the grid to theelectrostatic layer at the location of the connection. .Iaddend. .Iadd.12. The filter of claim 11, wherein the filter comprises a plurality ofsaid connections formed by applied heat and pressure to the filter mediaat the locations of the connections. .Iaddend. .Iadd.
 13. The filter ofclaim 12, wherein the stiffening grid includes intersecting legsestablishing the interstices. .Iaddend. .Iadd.14. The filter of claim13, wherein the filter media has a peripheral edge, and furthercomprising a frame embracing the peripheral edge of the filter media..Iaddend. .Iadd.15. The filter of claim 13, wherein the connections arelocated at intersections of the legs, such that the electrostatic layeris permanently attached to the grid at the intersections. .Iaddend..Iadd.16. The filter of claim 15, wherein the connections comprisebuttons located at the intersections. .Iaddend. .Iadd.17. The filter ofclaim 16, wherein the distal ends of pins comprise said locations ofsaid applied heat and pressure at the intersections. .Iaddend. .Iadd.18.The filter of claim 11, wherein the filter media further comprises asecond electrostatic layer permanently attached to a second grid, thefirst electrostatic layer and first grid being positioned parallel tothe second electrostatic layer and second grid, and a center padinterposed therebetween. .Iaddend. .Iadd.19. The filter of claim 18,further comprising a frame positioned to hold the first and secondelectrostatic layers in contact with opposite sides of the center pad,and the first and second grids are disposed on opposite outer sides ofthe filter media. .Iaddend. .Iadd.20. The filter of claim 13, whereinthe interstices comprises a multiplicity of squares. .Iaddend. .Iadd.21.An air filter for use in forced air systems, comprising:a filter mediafor filtering air, the filter including at least a first thermoplasticelectrostatic filter and at least a first thermoplastic stiffening gridhaving interstices for the passage of air therethrough; and a pluralityof heat and pressure formed buttons that attach the grid to theelectrostatic filter at the locations of the buttons. .Iaddend..Iadd.22. The filter of claim 21, further comprising a plurality of pinsextending from the grid through the electrostatic filter, wherein saidpins comprise said locations of said applied heat and pressure to saidbuttons. .Iaddend. .Iadd.23. The filter of claim 21, wherein thestiffening grid includes intersecting legs establishing the interstices..Iaddend.